This invention relates to apparatus for severing billets for use in an extrusion press.
An aluminum billet, for example, conventionally used in an extrusion press is cut to have a predetermined length and heated to a suitable temperature. However, since this method tends to waste the billet and is uneconomical, it is the present day practice to preheat a long billet in a furnace and then severe the billet to desired cut length on the outside of the furnace. In a prior art severing device utilized to severe a long preheated billet into desired lengths, for example in the apparatus disclosed in U.S. Pat. No. 3,348,441, adjacent cylindrical stationary die and cylindrical movable die slidable in the vertical direction in contact with the stationary die are disposed on the same horizontal axis, the billet is inserted into the openings of these cylindrical dies and the movable die is slid in the vertical direction to severe the billet. Accordingly, it has been difficult to design the stationary die and the movable die to have cylindrical openings of the same size and shape as the cross-section of billets to be severed so that it has been inevitable to form a small gap between the inner surface of the movable and stationary dies and the outer surface of billet. This is caused by the fact that it is necessary to make the inner diameters of the dies to be larger than the outer diameter of the billet for the purpose of readily inserting the billet into the openings. Where there is a gap between the inner surfaces of the stationary and movable dies and the billet, as the billet is severed by sliding the movable die, the cross-sectional configuration of the severed billet becomes eliptical to an extent corresponding to the gap between the inner surfaces of the dies and outer surface of the billet and the severed end is rounded. Due to the fact that a continuously cast aluminum billet is usually used for an extrusion press, the outer diameter of the billet is not so accurately finished as by machining, it is impossible to avoid the formation of the gap between the inner surfaces of the dies and the billet. For this reason, it has been necessary to increase the thickness of the dies so as to increase the clamping width for the billet thus preventing decrease in the severing capability.
When the sectional configuration of the severed billet becomes eliptical or the severed end surface is not perpendicular to the axis of the billet or rounded, an eccentric load will be applied to an extension stem utilized to extrude the billet thus breaking the stem. When the severed surface is irregular, air will be entrapped during the extrusion step thereby degrading the quality of the extruded products.
When severed by a shear action, the severed surface tends to contract in the severing direction but to expand in a direction perpendicular to the direction of severing with the result that an eliptical shape is formed. To minimize such deformation, it is advantageous to use dies that clamp the billet without gap at the time of severing. On the other hand, when inserting or withdrawing the billet from the dies, the billet should not be clamped by the dies and a gap should be formed between the billet and the dies.
In order to satisfy these contradictory conditions, as has been disclosed in Japanese utility model publication No. 13024/1972, it has been proposed to divide a cylindrical stationary die into a semicircular stationary die having an inner surface with the same radius of curvature as the outer diameter of the billet and a semicircular first movable die and further to divide a cylindrical movable die into second and third semicircular movable dies each having an inner surface of the same radius of curvature as the outer diameter of the billet. During severing, the dividing surfaces of the dies are closely fitted together and closely fitted to the billet and the dies are separated from the billet before and after the severing step. According to this proposal, the direction of clamping of the dies of the billet and the direction of severing are in the same direction, that is in the vertical direction. Accordingly, at the time of severing, the severing plane tends to expand in a direction perpendicular to the direction of severing so that when the billet remaining in the stationary dies is withdrawn therefrom after severing and when the billet is reinserted into the stationary dies after being reheated in the furnace, the flared portion of the billet will prevent smooth insertion of the billet into the ends of the stationary dies, thereby making it difficult to smoothly and correctly insert and clamp the billet.
To solve this problem, the same applicant as the present application has proposed an improved billet severing apparatus in which each of the stationary and movable dies is divided into two parts and the direction of clamping of the divided dies is made to be perpendicular to the direction of severing (laid open specification of Japanese utility model application No. 87935/1973). In this apparatus, since both of the stationary and movable dies are divided into two semicircular dies separable in the horizontal direction for clamping the billet frpm both sides and the movable die is slid in the vertical direction for severing the billet it is possible to obviate above described difficulty in which the severed plane spreads in a direction perpendicular to the direction of severing and to readily insert the remaining billet into the dies. With this apparatus, however, since the clamping of the separable semicircular dies of stationary and movable die assemblies is effected by a large vertical clamping cylinder mounted on the top of the apparatus for the purpose of decreasing the number of the clamping cylinders, the height of the apparatus is unduly increased. Moreover, as the billet is clamped by the vertical stroke clamping cylinder through a wedge mechanism, the construction of the clamping mechanism for the semicircular separable dies is complicated. The conventional billet severing apparatus is generally of the vertical type so that it is necessary to use an elaborate equipment for installing the apparatus. As above described, the height of the apparatus is increased because the vertical clamping cylinder is mounted on the top of the apparatus. Moreover, as it is necessary to provide a vertical shear cylinder beneath the apparatus for vertically moving the movable die. For this reason, it is necessary to form a vertical hole through the floor bed for accommodating the vertical shear cylinder, thus complicating the installation operation and increasing the cost of installation.